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Introduction. The article considers the issues of operation of circulating pumps of autonomous heat supply systems when the heating circuit is filled with antifreezing coolants. It is possible to remotely start up a heating system cooled down to –15 °С. Ethylene glycol and propylene glycol antifreeze have been studied as antifreeze carriers. Flow-rate characteristics, power efficiency coefficients are studied for “wet rotor” circulation pumps in versions of electric motors of asynchronous type with constant rotor speed and energy-saving pumps on permanent magnets. Materials and methods. The research was carried out on test stands. Wall-mounted gas boilers and electric boilers witha rated capacity up to 24 kW were used as heat generators. Circulation motors, control hydraulic valves, part of the pipes with a length of 6 meters were located in a separate freezer. The pumps and parts of the heating circuit were kept at subzero temperatures for 2 hours before the system was started up Results. Pressure and flow characteristics of two types of pumps, energy efficiency coefficients were obtained, comparisons with water coolant are provided, the influence of electric network voltage on the investigated parameters was determined. Conclusions. The research has shown the possibility of starting circulating pumps in a refrigerated condition with a temperature of –15 °С. Remote start of the cooled heating system with circulation circuit filling with antifreeze when using hydrocarbon fuel boilers is not possible. Operation of heating systems with non-freezing coolants in the operation temperature ranges of 20–80 °C requires changing in settings of the combustion process and a significant increase inthe circulation pump head in comparison with the coolant water.

We report on single photon emitters for the green-yellow spectral range, which comprise a CdSe/ZnSe quantum dot placed inside a semiconductor tapered nanocolumn acting as a multimode nanoantenna. Despite the presence of many optical modes inside, such a nanoantenna is able to collect the quantum dot radiation and ensure its effective output. We demonstrate periodic arrays of such emitters, which are fabricated by focused ion beam etching from a II-VI/III-V heterostructure grown using molecular beam epitaxy. With non-resonant optical pumping, the average count rate of emitted single photons exceeds 5 MHz with the second-order correlation function g(2)(0) = 0.25 at 220 K. Such single photon emitters are promising for secure free space optical communication lines.

The fine structure of the exciton spectrum, containing optically allowed (bright) and forbidden (dark) exciton states, determines the radiation efficiency in nanostructures. We study time-resolved micro-photoluminescence in MoS$_2$ monolayers and bilayers, both unstrained and compressively strained, in a wide temperature range (10-300 K) to distinguish between exciton states optically allowed and forbidden, both in spin and momentum, as well as to estimate their characteristic decay times and contributions to the total radiation intensity. The decay times were found to either increase or decrease with increasing temperature, indicating the lowest bright or lowest dark state, respectively. Our results unambiguously show that, in an unstrained monolayer, the spin-allowed state is the lowest for a series of A excitons (1.9 eV) with the dark state being < 2 meV higher, and that the splitting energy can increase several times at compression. In contrast, in the indirect exciton series in bilayers (1.5 eV), the spin-forbidden state is the lowest, being about 3 meV below the bright one. The strong effect of strain on the exciton spectrum can explain the large scatter among the published data and must be taken into account to realize the desired optical properties of 2D MoS$_2$.

Nanotubes (NTs) of transition metal dichalcogenides (TMDs), such as MoS2 and WS2, were first synthesized more than a quarter of a century ago; nevertheless, many of their properties have so far remained basically unknown. This review presents the state of the art in the knowledge of the optical properties of TMD NTs. We first evaluate general properties of multilayered TMD crystals, and analyze available data on electronic band structure and optical properties of related NTs. Then, the technology for the formation and the structural characteristics of TMD NTs are represented, focusing on the structures synthesized by chemical transport reaction. The core of this work is the presentation of the ability of TMD NTs to emit bright photoluminescence (PL), which has been discovered recently. By means of micro-PL spectroscopy of individual tubes we show that excitonic transitions relevant to both direct and indirect band gaps contribute to the emission spectra of the NTs despite the presence of dozens of monolayers in their walls. We highlight the performance of the tubes as efficient optical resonators, whose confined optical modes strongly affect the emission bands. Finally, a brief conclusion is presented, along with an outlook of the future studies of this novel member of the family of radiative NTs, which have unique potential for different nanophotonics applications., 38 pages, 11 fugures, 106 references

Quasi-2D GaN layers inserted in an AlGaN matrix are proposed as a novel active region to develop a high-output-power UV light source. Such a structure is successfully achieved by precise control in molecular beam epitaxy and shows an amazing output power of ≈160 mW at 285 nm with a pulsed electron-beam excitation. This device is promising and competitive in non-line-of-sight communications or the sterilization field.

International audience; Emerging part of condensed matter science, which deals with the systems of extreme two-dimensionality, renews the interest in natural 2D objects such as planar stacking faults (SFs) in semiconductor crystals. We report on the observation of an excitonic state localized at the 1D intersection of the SF with a high quality ZnSe quantum well (QW). The micro-photoluminescence measurements are performed in a specimen used for preceding transmission electron microscopy studies. We demonstrate that the observed narrow lines are polarized along SFs and their linewidths depend on the SFs length. For short SFs, the linewidth can be as low as 0.15 meV. Using the combination of the effective mass approach and the density functional theory calculations we show that the exciton localization is due to the intrinsic electric field inside the SF, which also leads to a spatial separation of electron and hole in the exciton. The 1D intersection of perfect natural and artificial 2D objects can serve as a promising playground for the study of subtle excitonic effects in single defects.

Upon alkylation of 2-aminoprop-1-ene-1,1,3-tricarbonitrile with phenacyl bromides, 2-(2-aryl-2-oxoethyl)-2-(5-aryl-3-cyano-1Н-pyrrol-2-yl)malononitriles are formed instead of previously presumed isomeric 2-(3,8-diaryl-6-oxo-2,7-diazaspiro[4.4]nona-2,8-dienes. The structure of 3-cyano-2-[2-(4-methoxyphenyl)-2-oxoethyl]-2-[5-(4-methoxyphenyl)-1Н-pyrrol-2-yl]malononitrile was studied by X-ray structural analysis.

This chapter covers a wide range of promising applications based on plasmonic effects in nanostructures comprising conductors and semiconductors. The ultimate goal of the chapter is to present the most amazing results yet obtained and to reveal existing bottlenecks in the field of the metal–semiconductor plasmonics. The list of most appealing advances described here includes achievement of the strong coupling regime in plasmonic cavities with both organic and inorganic semiconductors, demonstration of the room-temperature operation of plasmonic nanolasers and single photon sources, preservation of the non-classical statistics of single photons during energy transfer by surface plasmon polaritons, employment of metal–semiconductor composites as active media of plasmonic solar cells, efficient wavefront engineering in the quantum cascade lasers with integrated plasmonic structures, and tuning the plasmon frequency in metallic structures by gated graphene in a broad frequency range. The presented discussions rely on the results obtained in all previous chapters.

This chapter presents a general description and calculation of the electronic band structures in III–V and II–VI semiconductors with both zinc-blende and wurtzite crystal structures. Relevant concepts are introduced, including the Bloch’s theorem and the symmetry theory based on the mathematics of group representations. Analytical expressions for the band dispersion around high-symmetry points of the Brillouin zone are obtained in the framework of the k⋅p theory. Kane and Luttinger–Kohn models are represented for the zinc-blende crystal structure, while the electronic band structure of the wurtzite-type semiconductors is defined within the Kane model and the model developed by Rashba, Sheka, and Pikus. Effects of elastic strain on the band structures are described. The basic principles of the band theory in crystals, outlined in this chapter, are employed in following chapters to define optical processes in semiconductor and metal–semiconductor nanostructures.

This chapter summarizes the fundamental facts and concepts of classical electromagnetism, applied in successive chapters to the consideration of the electronic plasma excitations supported by various metal and metal–semiconductor nanostructures. The chapter outlines the basic principles of electrodynamics, the Drude theory describing dielectric function of free electrons, propagation of surface plasmon polaritons at a plane interface between a metal and an insulator, and excitation of localized surface plasmons in metal particles. The quasi-static approximation is represented for the general case of ellipsoidal particles, whereas the exact Mie theory is employed to define plasmonic excitations in conducting spheres. Thus, the goal of the chapter is to give a basic overview of the plasmonic effects and to introduce notations, conventions, and units of electrodynamics that are consistently used throughout the rest of the book.

This chapter describes the long history of plasmonics, starting from the Lycurgus cup and stained glass windows that rely on plasmonic properties of tiny metallic particles and Wood’s anomalies in light reflection from a metal diffraction grating. The chapter outlines the fundamental contributions to the scientific background of plasmonics of such outstanding scientists as Zenneck, Sommerfeld, Mie, Fano, Van der Pol, Fock, Purcell, Ritchie, and many others, who developed the concepts of surface plasmon polaritons and localized surface plasmons, as well as the foundations of the resonant interaction of light with conductors. The successive discovery of the phenomenon of surface enhanced Raman scattering (SERS) stimulated applications of plasmonic effects in modern optical spectroscopy. It is emphasized that most recent breakthroughs of plasmonics essentially rely on the development of nanotechnology and nanometrology. Apart from a short historical survey, the chapter describes the scope of the book and defines the potential readership.

This chapter is concerned with a description of the main electromagnetic effects causing enhancement of optical absorption and optical emission in metal–semiconductor nanostructures. To this end, the chapter considers a pure electromagnetic mechanism, which relies on plasmon-induced enhancement of both local optical field intensity and density of photonic modes in the vicinity of a metal object. Relevant concepts are introduced and practical calculations of the electromagnetic enhancement in simplified model structures are presented. In particular, the classical electromagnetic problems are treated analytically for a plane metal–semiconductor interface and a metal sphere embedded into a semiconductor medium. The quasi-static approximation is employed to highlight the effects of the shape of the metallic object. The presented plots and diagrams, calculated within the analytical models, can be used to estimate the enhancement in real metal–semiconductor structures.

This chapter covers the optical and electronic properties of available conducting materials capable of supporting plasmonic excitations. Described here are noble metals and polyvalent metals (gold, silver, indium, and aluminium), degenerate semiconductors, doped oxides and semimetals, as well as graphene. The area of applicability of the considered materials for plasmonics is determined on the basis of their complex dielectric functions defined by both interband and intraband transitions. The properties of metal–dielectric composites are treated in the framework of the generalized Maxwell–Garnett approximation. The influence on fundamental parameters of semiconductor compounds of their deviation from stoichiometry is discussed in terms of the empirical tight binding theory. Where possible, the chapter provides explicit expressions and plots defining the spectra of complex dielectric functions and other important characteristics.

This chapter introduces the physics of semiconductor heterostructures and nanostructures. The electronic and optical properties of the most common III–V and II–VI binary semiconductor compounds and their alloys are presented and discussed. The concept of pseudomorphic heterostructures comprising strained layers of these materials is introduced and the basic effects of spatial confinement are considered, focusing on two-dimensional structures (quantum wells) and zero-dimensional structures (quantum dots). In both cases the electron spectra and optical transitions are defined in the framework of a multiband envelope function approximation. Excitonic fine structure is represented both in quantum wells and quantum dots in terms of the symmetry reduction induced by the carrier confining potential. The relationships presented in the chapter allow one to predict the energy and strength of optical transitions, depending on sizes and shapes of semiconductor nanostructures; they can be used to justify the choice of particular nanostructures for the purposes of plasmonics.

This chapter describes basic optical processes in semiconductor crystals, including interband optical absorption, gain, and emission. The consideration is performed for the two types of crystal structures, zinc-blende and wurtzite, in the framework of a semi-classical approach when the electromagnetic field is treated classically while the electrons are described by the quantum mechanical Hamiltonian and wave functions. Einstein coefficients are introduced in order to define the connection between absorption, stimulated emission, and spontaneous emission. Optical selection rules are obtained in the framework of the k⋅p theory by calculating the interband momentum matrix elements. The concepts of Wannier–Mott excitons and exciton polaritons are discussed in the framework of the effective mass approximation for the case of the direct band-gap semiconductors. The chapter establishes the symmetry classification of excitonic states in the semiconductor crystals in terms of the theory of irreducible group representations.

AlGaN-based SQW heterostructures grown by plasma-assisted molecular beam epitaxy on c-Al2O3 substrates have been studied with high resolution transmission electron microscopy (HR TEM), photoluminescence spectroscopy and x-ray diffraction. The high-temperature (780°C) synthesis of the AlN buffer layer nucleated on c-Al2O3 by a migration enhanced epitaxy and including several ultra-thin GaN interlayers grown under moderate N-rich conditions was shown to be the optimum approach for lowering the threading dislocations density down to 108-109 cm-2. HR TEM study has confirmed the fine structure of single quantum wells (SQW) formed by a sub-monolayer digital alloying technique and revealed different kinds of compositional inhomogeneities in the AlxGa1-xN barrier layers of the heterostructures, including the formation of Al-rich barriers induced by the temperature-modulated epitaxy and the spontaneous compositional disordering along the growth axis for x=0.6-0.7. The influence of these phenomena on the parameters of the mid-UV stimulated emission observed in the SQW structures has been studied as well.

The 14th International Conference on II–VI Compounds was held in Saint-Petersburg, Russia, on 23–28 August 2009. The meeting continued a series of biennial conferences, which was started in Durham, UK, in 1983. The preceding conference was held on Jeju Island, Korea, in 2007. The 14th conference was organized by the Ioffe Physico-Technical Institute of the Russian Academy of Sciences. The attendance of the conference was most world-wide as compared with 2005 and 2007, although the number of participants was less than in 2007. The conference brought together 257 scientists from 26 countries, with Germany and Russia sharing a leadership in numbers. Seventy of them were young scientists. From 252 abstracts submitted, the Program Committee selected 237 for presentation, including 59 oral papers. In addition, 24 invited papers were proposed. All the invited and oral papers were presented, and 178 posters were displayed during three poster sessions. Besides, a special Session of Review Lectures was organized at the beginning with participation of most prominent scientists in the field: Le Si Dang (Institut Neel CNRS, France), Alexey Ekimov (Nanocrystal Technology Co., USA), Jacek Furdyna (University of Notre Dame, USA), Claus Klingshirn (University of Karlsruhe, Germany). The present proceedings volume of physica status solidi includes 124 papers from the conference accepted for publication. The conference program reflects a revival of interest in the recent years to this group of materials due to the emergence of many fascinating ideas and prospects as well as the development of new technologies. In particular, the wide bandgap semiconductors like ZnO, (Zn,Cd)Te, (Zn,Cd)Se provide unique opportunities to exploit the ideas of photonic band engineering in specially designed quantum nanostructures. This intense activity has yet resulted in the observation of numerous original effects and emergence of new device concepts, including Bose condensation of exciton–polaritons (“polariton laser”), triggered single-photon sources for quantum cryptography, optical switches and memories. Important areas that take advantage of the specific properties of II–VI compounds are quantum information processing and spintronics. Among other prospective practical applications of the II–VI compounds presented at the conference are yellow-to-blue lasers, infrared detectors, terahertz emitters, inter-subband electroluminescence devices, and nanoscale sensors. During the conference, the Complimentary Session was held to mark the 80th birthday of Prof. Gottfried Landwehr, outstanding German physicist and Honorary Chair of the Conference, who initiated fundamental research on semiconductors in high magnetic fields, and later contributed a lot to the development of physics and technology of II–VI compounds world-wide. The Editors would like to thank all the members of the International Advisory Committee and the International Program Committee for their encouragement and great help during the conference organization. We are grateful to the referees for their effort and time devoted to the paper review process. We appreciate very much the managers and technical staff of the Hotel “Saint-Petersburg” as well as the young researchers and Ph.D. students from the Ioffe Institute for their assistance before and during the conference. We owe our best thanks to the sponsors of the conference listed on the following pages for their substantial support. We would also like to express our sincere gratitude to Dr. Stefan Hildebrandt, Managing Editor of physica status solidi, for his friendly assistance, understanding and patience in the editorial process. The next International Conference on II–VI Compounds will be held in September 2011 in Riviera Maya, Mexico. We wish the organizers a gorgeous and successful meeting (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper reports on two plasmonic systems based on III-Nitrides: (i) InGaN - Au nanoparticles; (ii) InN with spontaneously formed buried In nanoparticles. By using NSOM and μ-PL studies we established necessary conditions for the efficient interaction of localized plasmons excited in a gold nanoparticle with localized excitons situated near the InGaN surface. The tens-fold PL intensity enhancement was observed for ~100 nm Au nanoparticles. The narrow lines of single excitons have been registered at low temperature. Due to specific thermodynamic properties of InN, its optical properties are strongly influenced by plasmons in spontaneously formed In nanoparticles. The μ-CL study of MBE grown InN/In structures with intentional periodic 0-48 ML In insertions has shown that the bright CL spots (peaked spectrally at ~0.7eV) coincide always with the agglomerates of In nanoparticles. The intensity increase by the factor of ~10 2 is in good agreement with calculations of the average enhancement factor in InN/In nanocomposites comprising the nanoparticles of an arbitrary shape and orientation. Time-resolved PL studies have demonstrated pronounced Purcell effect, i.e. significant shortening of spontaneous recombination rate, in both systems. Terahertz emission (~3 THz) observed in InN epilayers under electrical pumping is ascribed to surface plasmon polariton waves coupled to electromagnetic field at quasi-periodical structural imperfections.

Electronic spin polarization up to 100 % has been observed in type‐II narrow‐gap heterostructures with InSb quantum dots in an InAs matrix via investigation of circular‐polarized photoluminescence at external magnetic field applied in Faraday geometry. Energy spectrum of holes confined in monolayer scale InSb/InAs quantum well is calculated using tight‐binding approach. The observed effect is explained in terms of strong Zeeman splitting of electrons in InAs matrix due to their large intrinsic g‐factor and corresponding optical transition selection rules. Temperature dependence of polarization degree well fit obtained data providing its experimental verification of suggested model.

Magnetoluminescence of $\mathrm{Cd}\mathrm{Mn}\mathrm{Se}\text{\ensuremath{-}}\mathrm{Zn}\mathrm{Se}$ disk-shaped quantum dots in a magnetic field up to $11\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ is measured in the Faraday and Voigt geometries at liquid He temperatures and various levels of laser excitation. Within the range of $B=0--11\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ the intensity of the quantum dot photoluminescence increases strongly (up to two orders of magnitude) in the Faraday geometry and only slightly ($\ensuremath{\sim}1.5$ times) in the Voigt geometry. To explain the observed dependence on magnetic field direction the selection rules for the Auger recombination of excitons with excitation of Mn-ion are revised. The magnetic field dependence of the quantum yield of quantum dot exciton emission and its anisotropy are shown to appear due to the dependence of Auger recombination of uncharged excitons with excitation of Mn-ion on the spin of both exciton and Mn-ion. The anisotropy is provided by a quick spin relaxation of photoexcited excitons into the ground state which spin structure depends on the direction of the magnetic field.

Stressor-controlled epitaxy has been proposed as an efficient method of CdSe quantum dot fabrication. The studies are performed on a type-II CdSe/BeTe system, where CdTe and BeSe inteface bonds play a role of intrinsic stressors. Predeposition of ~0.2 ML CdTe stressor ( Δ a/a= +15%), corresponding to a local maximum of RHEED specular spot intensity, appears to induce variation of stress field across the BeTe surface, caused by alternating regions with CdTe and BeSe bonds. It results in preferential nucleation of regularly arranged CdSe QDs at the BeSe sites with the following vertical chess-ordering in the CdSe/BeTe multilayers. The structures demonstrate bright up to RT PL in the 1.9-2.1 eV range and strong in-plane PL anisotropy related to non-equivalent bottom and top CdSe QD interfaces having estimated from x-ray diffraction total concentrations of CdTe and BeSe bonds of 0.3-0.4 and 0.6-0.7 ML, respectively.